 Eruptions associated with subducting zones, meanwhile, are driven by subducting plates that add volatiles to the rising plate, lowering its melting point.Each process generates different rock; mid-ocean ridge volcanics are primarily basaltic, whereas subduction flows are mostly calc-alkaline, and more explosive and viscous.Spreading rates along mid-ocean ridges vary widely, from per year at the Mid-Atlantic Ridge, to up to along the East Pacific Rise.